1. Field of the Invention
This invention relates to a method and a device for the removal of particles, in particular particles of soot, from the exhaust of internal combustion engines, whereby the particles are electrostatically charged by means of at least one electrode, some of the particles form agglomerates, and the particles and/or particle agglomerates are separated by means of one or more filters, as well as a device for the removal of particles, in particular soot particles, from the exhaust of internal combustion engines, whereby the device comprises a housing with a feed line and a discharge line for the exhaust, at least one electrode which is connected to a high voltage source for the electrostatic charging of the particles, and a filter body.
2. Description of the Prior Art
The reduction of particulate emissions in exhaust gases plays a major role in efforts to further reduce pollution caused by exhaust gases from internal combustion engines, in particular from Diesel engines. Numerous attempts have therefore been made to remove the particulate emissions, in particular particles of soot, which are contained in exhaust gases.
A survey of the prior art has identified the publication "Rul.beta.filtertechnik fur Stadtlinienbusse", Internationales Verkehrswesen ["Soot Filter Technology for Municipal Buses", International Transportation], 40 (1988), Volume 1, January/February. Ceramic monolith filters, filter candles with a filter means made of ceramic or wire mesh or filters wound with ceramic yarn or a combination of an electric coagulator and a downstream cyclone are used to remove particulates.
In the last-named system for the removal of particles, an agglomeration of the particles takes place in the electric coagulator, so that the particles can then be removed in the downstream cyclone, taking advantage of the centrifugal force on the particles in the receiving chamber of the cyclone, while the gas current is emitted through the submerged tube of the cyclone as clean gas into the exhaust. In this particle-removal system, however, it is necessary to make separate arrangements for the disposal of the particles removed.
When filters are used, a regeneration or replacement of the filter is necessary, since the particles which have been removed clog the filter, and the pressure loss caused by the filter increases as the filter charge increases. The regeneration is performed by burning away the particles at temperatures which are above the ignition temperature of the soot. Since this temperature is not reached in exhaust gases from internal combustion engines, or is reached only during full load operation, either the exhaust gas temperatures must be increased by motor-driven measures, or the ignition temperature of the exhaust must be reduced by additives added independently to the fuel, to the intake air or to the exhaust, or by catalytic coatings on the filter. An additional possibility is a forced regeneration by the application of heat, e.g. by means of burners.
Metal filters, such as filters made of wire mesh, have the disadvantage of a reduced high-temperature strength, which is insufficient for the removal of particulates from the above-mentioned exhaust gases. In particular, filters made of such material are unsuitable for a thermal regeneration.
U.S. Pat. No. 4,406,119 discloses a method for the removal of particles from the exhaust flow of internal combustion engines, whereby the particles are negatively charged by means of an electrode with a high voltage of 10-20 kV, some of the particles form agglomerates and are separated by means of a filter and a downstream cyclone or heating element. The filters consist of porous ceramic or metal meshes or tissues.
EP-A-0 425 433 discloses a process in which charged soot particles are filtered out in at least one filter with opposite polarity. The filter material consists of an open-pore network structure made of fibers or a base structure which has high temperature resistance, whereby the network structure is designed in the form of foam, porous sinter, fiber tissues, braided fibers, non-woven tissue or loose bundles of fibers, and consists of electrically conducting fibers, fibers provided with an electrically conducting coating, or of such a basic structure. Electrically conducting fibers or basic structures of the filter materials can consist of metals, e.g. stainless steel.
JP-A-59 145 314 discloses an apparatus with a high voltage electrode for the generation of an electrostatic field and a collector made of foamed steel as a counter electrode to trap the electrically charged particles.
EP-A-0 244 061 discloses a method for the regeneration of a filter loaded with combustible particles of a Diesel engine exhaust, whereby an electrical current is conducted through the loaded filter, and the filter is thereby heated above the ignition temperature of the particles. Several filters are operated-simultaneously in the exhaust flow. During the regeneration, the exhaust gas does not flow through the filters.
The object of the invention is therefore to create a method and a device of the type indicated above which make it possible in a simple manner to effectively remove particulates from the exhaust gases of internal combustion engines, in particular of land vehicles or water craft operated with internal combustion engines, without thereby adversely affecting the mobility of the vehicles. During the removal of the particles, it should be possible to regenerate the filters during the operation of the internal combustion engine.